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CHAPTER
35
Special Senses
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35-2
Learning Outcomes (cont.)
35.1 Describe the anatomy of the nose and the
function of each part.
35.2 Describe the anatomy of the tongue and the
function of each part.
35.3 Describe the anatomy of the eye and the
function of each part, including the accessory
structures and their functions.
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35-3
Learning Outcomes (cont.)
35.4 Explain the visual pathway through the eye
and to the brain for interpretation.
35.5 Describe the causes, signs and symptoms,
and treatments of various disorders of the
eyes.
35.6 Describe the anatomy of the ear and the
function of each part, and the role of the ear
in maintaining equilibrium.
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35-4
Learning Outcomes (cont.)
35.7 Explain how sounds travel through the ear
and are interpreted in the brain.
35.8 Describe the causes, signs and symptoms,
and treatments of various disorders of the
ears.
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35-5
Introduction
• Special senses – receptors in the head
–
–
–
–
Nose
Tongue
Eyes
Ears
• Touch is a generalized sense
• Stimulus  nervous system  brain 
response
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35-6
The Nose and the Sense of Smell
• Olfactory receptors
– Chemoreceptors – respond to changes in
chemical concentrations
– Chemicals must
be dissolved
in mucus
– Located in the
olfactory organ
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35-7
The Nose and the Sense of Smell (cont.)
Activation of smell receptors 
information sent to olfactory nerves
The information is sent along
olfactory bulbs and tracts
Cerebrum – interprets information
as a type of smell
Sensory Adaption
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35-8
Apply Your Knowledge
You notice an odor coming from a patient when
you enter the exam room. Why would the patient
not be able to smell it?
ANSWER: After a few minutes, smell receptors undergo
sensory adaptation and no longer respond to the chemical,
and the patient can no longer smell the odor.
Very
Good!
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35-9
The Tongue and the Sense of Taste
• Gustatory receptors – on the taste buds
• Taste buds
– Papillae of the tongue
– Roof of mouth
fewer than on tongue
– Walls of throat
}
Tongue
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35-10
The Tongue and the Sense of Taste (cont.)
• Taste buds
– Taste cells ~ chemoreceptors that react to
chemicals in food and drink must be
dissolved in saliva to activate
– Supporting structures ~ fill in space
Tongue
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35-11
The Tongue and the Sense of Taste (cont.)
• Taste sensations
• Umami
– Sweet – tip
– 5th basic taste
– Sour – sides
– Glutamate
– Salty – tip and
sides
– Bitter – back
• Spicy foods
– Activate pain
receptors
– Interpreted by brain
as “spicy”
Tongue
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35-13
The Tongue and the Sense of Taste (cont.)
Taste sensation
Activation of
taste cells
Cranial
nerves
Gustatory cortex of cerebrum
interprets information as
a particular taste
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35-14
Apply Your Knowledge
What are the four primary taste sensations and
where are their corresponding taste cells
located?
ANSWER: The four primary taste sensations are:
Sweet – concentrated on the tip of the tongue
Sour – concentrated on the sides of the tongue
Salty – concentrated on the tip and sides of the tongue
Bitter – concentrated on the back of the tongue
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35-15
The Eye and the Sense of Sight
• Vision system
– Eyes
– Optic nerves
– Vision centers in
the brain
– Accessory
structures
• Eye
– Processes light to
produce images
– Three layers
– Two chambers
– Specialized parts
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35-16
The Eye and the Sense of Sight (cont.)
• Outer Layer
– Cornea
– Sclera
• Tough outer layer
• Transparent
• Light cannot pass
through the sclera
• “Window” that
allows light into eye
• Sense receptors
– Limbus ~ cornealscleral junction
Eye
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35-17
The Eye and the Sense of Sight (cont.)
• Middle layer – choroid
– Contains blood vessels
– Iris
• Muscle tissue relaxes and contracts to alter the
size of the pupil
• Regulates the amount of light entering the eye
Eye
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35-18
The Eye and the Sense of Sight (cont.)
• Middle layer (cont.)
– Ciliary body ~ wedge-shaped muscles that
controls the shape of the lens
– Lens
• Changes shape to focus light on retina
• Accommodation – the ability of the lens to change
shape
Eye
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35-19
The Eye and the Sense of Sight (cont.)
• Inner layer – retina
– Optic disc – optic nerve enters retina
– Rods
• Sensitive to light
• Function in dim light – “night” and peripheral vision
• Do not provide sharp image or detect color
Eye
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35-20
The Eye and the Sense of Sight (cont.)
• Inner layer (cont.)
– Cones
• Function in bright light
• Sensitive to color and provide sharp images
• Enable differentiation of tones and hues of color
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35-21
The Eye and the Sense of Sight (cont.)
• Anterior chamber of the eye
– Front of lens
– Filled with aqueous humor – nourishes and bathes
anterior eye
• Posterior chamber
– Behind lens
– Contains vitreous humor – maintains shape of eyeball
and keeps the retina flat
Eye
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35-23
Visual Accessory Organs
• Eye orbits – form a protective shell
around the eyes
• Eyebrows protect eyes
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35-24
Visual Accessory Organs
• Eyelids
– Skin, muscle, and connective tissue
– Blinking
• Prevents surface from drying out
• Keeps foreign material out of eye
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35-25
Visual Accessory Organs (cont.)
• Conjunctivas –
produce mucus to
keep the surface of
the eyeball moist
• Lacrimal
apparatus
– Lacrimal glands ~
produce tears
– Nasolacrimal ducts
~ drain tears into
nose
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35-26
Visual Accessory Organs (cont.)
• Extrinsic eye muscles
– Six per eye
– Move the eye
Levator palpebrae
superioris (cut)
Trochlea
Superior oblique
Superior rectus
Optic Nerve
Lateral rectus
Inferior Rectus
Inferior oblique
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35-27
Apply Your Knowledge
Matching: ANSWER:
___
G Middle layer of eye
H Eye sockets
___
F Controls shape of lens
___
___
D Outer layer of eye
___
B Anterior chamber
A Tears
___
___
I Ability of lens to
change shape
E Posterior chamber
___
C Inner layer of eye
___
A.
B.
C.
D.
E.
F.
G.
H.
I.
Lacrimal glands
Aqueous humor
Retina
Sclera
Vitreous humor
Ciliary body
Choroid
Orbits
Accommodation
Out of
Sight!
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35-28
Visual Pathways
• Eye works like a camera
– Light enters the eye through the lens
– Refraction – bending of light to focus it on the
retina
– Projected upside down on the retina
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35-29
Visual Pathways
Image upside
down on retina
Retina converts
light to nerve
impulse
Image turned
right-side up
Optic
nerve
Optic
chiasm
Occipital
lobe of
cerebrum
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35-30
Apply Your Knowledge
What is refraction and which part of the eye
carries out refraction?
ANSWER: Refraction is the bending of light that enters
the eye to focus it on the retina. The cornea performs
this function.
Well
done!
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35-31
The Aging Eye
• Tears altered
• Eyes dryer
• Lens more rigid
• Retinal changes
• Less adaptable to
light
• Impaired night and
peripheral vision
• Impaired depth
perception
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35-32
Common Diseases and Disorders
Disorder/Disease
Description
Astigmatism
Cornea or lens has
abnormal shape; blurred
images
Results from a decreased
production of the oil within
the tears
Eversion of lower eyelid
Dry eye syndrome
Ectropin
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35-33
Common Diseases and Disorders
Disorder/Disease
Description
Entropion
Inversion of lower eyelid
Nystagmus
Rapid, involuntary eye
movements
Layers of retina separate;
medical emergency
Retinal
detachment
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35-34
Apply Your Knowledge
What vision changes can occur in the elderly
patient?
ANSWER: An elderly patient may have difficulty
seeing because of drooping eyelids. Focusing may
be more difficult because less light enters the eye.
He may have difficulty distinguishing colors due to
yellowing of the lens. Vision may be fuzzy because
of changes in the retina. Night vision can become
impaired. The patient may see floaters or “sparks.”
Nice job!
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35-35
The Ear and Senses of Hearing and
Equilibrium
• External ear
– Auricle (pinna) - collects sound waves
– External auditory canal
• Lined with hairs and glands that produce cerumen
• Guides sound wave to the tympanic membrane
which separates external ear and middle ear
Ear
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35-36
The Ear and Senses of Hearing and
Equilibrium (cont.)
• Middle ear
– Ear ossicles
– Ossicles
• Malleus
• Vibrate
• Incus
• Hit the oval
window
• Stapes
Ear
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35-37
The Ear and Senses of Hearing and
Equilibrium (cont.)
• Middle ear (cont.)
– Eustachian tube
• Connects middle ear to throat
• Equalizes pressure on eardrum
– Oval window – separates middle ear from
inner ear
Ear
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35-39
The Ear and Senses of Hearing and
Equilibrium (cont.)
• Inner ear – labyrinth of communicating
chambers
– Semicircular canals ~ equilibrium
– Vestibule ~ equilibrium
– Cochlea
• Hearing receptors
• Organ of Corti – organ of hearing
Inner
ear
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35-41
The Ear and Senses of Hearing and
Equilibrium (cont.)
Fluid moves in
semicircular
canals and
vestibule
Activates
equilibrium and
hearing receptors
Head movement
Cerebrum interprets
information and
advises the body to
make adjustments
Vestibular nerves
transmit
information
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35-42
Apply Your Knowledge
Matching:
ANSWER:
___
E Pinna
A.
Organ of Corti
___
C Malleus, incus, and stapes
B.
Cerumen
___
F Hearing receptors
C.
Ear ossicles
___
G Inner ear
D.
Tympanic membrane
___
A Organ of hearing
E.
Auricle
___
B Earwax
F.
Cochlea
___
D Eardrum
G. Labyrinth
___
H Detect balance of body
H.
Semicircular canals
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35-43
The Hearing Process
• External ear
– Collect sound waves
– Channels waves to the tympanic membrane
– Tympanic membrane vibrates
• Middle ear – ossicles amplify
vibrations
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35-44
The Hearing Process (cont.)
• Inner ear
– Amplified waves bend hairs lining cochlea
– Movement of hairs trigger nerve impulses
– Impulses are transmitted by auditory nerve to
the brain for interpretation
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35-45
The Hearing Process (cont.)
• Bone conduction
– Alternate sound pathway to inner ear
– Bones of the scull conduct sound waves
• Identification of hearing
problems
– Normal bone conduction
– Problem likely in middle or
external ear
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35-46
Apply Your Knowledge
How do we hear?
ANSWER: Sound waves are collected by the external ear
and are funneled down the ear canal to the tympanic
membrane. The waves make the tympanic membrane
vibrate. The ossicles amplify these vibrations which
enter the inner ear and cause movements of the hairs
that line the cochlea. These movements trigger nerve
impulses which are sent to the brain via the auditory
nerve. The brain perceives the impulses as sound.
Great
Answer!
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35-47
The Aging Ear
• External ear
– Larger
– Cerumen drier
– Canal narrows
• Middle ear
– Eardrum shrinks
– Joints between ossicles degenerates
• Inner ear – less sensitive to position
changes
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35-48
How to Recognize Hearing Problems in
Infants
• Infants to 4 months
– Startled by loud noises
– Recognize mother’s voice
• 4 to 8 months
– Regularly follow sounds
– Babble at people
• 8 to 12 months
– Respond to the sound of
their name
– Respond to “no”
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in any manner. This document may not be copied, scanned, duplicated, forwarded, distributed, or posted on a website, in whole or part.
35-49
Common Diseases and Disorders of the
Ear
Disorder/Disease Description
Acoustic
Neuroma
Cerumen
impaction
Benign tumor of the cranial
nerve involved in hearing and
balance; commonly causes
gradual hearing loss in one ear
Build up of wax within external
auditory canal with some degree
of hearing loss due to blocked
sound waves
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in any manner. This document may not be copied, scanned, duplicated, forwarded, distributed, or posted on a website, in whole or part.
35-50
Common Diseases and Disorders of the
Ear
Disorder/Disease Description
Hearing loss
Deafness; the loss of the ability
to hear sounds at normal levels.
Conductive – blockage of sound
waves
Sensorineural – damage to
auditory nerve
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35-51
Common Diseases and Disorders of the
Ear (cont.)
Disorder/Disease
Description
Otitis
Otitis externa
Otitis media
Otitis interna
Inflammation of the ear
Swimmers’ ear
Middle ear infection; common
infection
Labyrinthitis; inner ear infection
Immobilization of the stapes;
common cause of conductive
hearing loss
Hearing loss due to aging process
Osteosclerosis
Presbycusis
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35-52
Apply Your Knowledge
ANSWER:
True or False:
externa
___
F Otitis media is also called swimmers’ ear.
T Presbycusis is hearing loss due to the aging process.
___
T Otitis interna is an inflammation of the labyrinth.
___
T Otosclerosis is the immobilization of the stapes.
___
F
Conductive hearing loss is caused by damage to the
auditory nerve. Sensorineural
T
Labyrinthitis often causes nausea and vertigo.
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35-53
In Summary
35.1 Olfactory receptors – the sense receptors for
the sense of smell – are found in the olfactory
organ located in the upper part of the nasal
cavity.
31.2 Gustatory receptors are found on the taste
buds, which are located on the papillae
(bumps) of the tongue.
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35-54
In Summary
35.3 The eye is composed of three layers. The sclera is the
outer protective layer and includes the cornea.
The middle vascular layer is the choroid consisting of
the iris, pupil, ciliary body, and lens, and is the area of
light regulation and focusing.
The innermost layer is the retina containing the rods
and cones, the optic nerve, and the optic disk. This is
where the nerve impulse is picked up and brought to
the brain for interpretation.
The accessory organs are the orbits, eyelids,
conjunctivas, lacrimal apparatus, and extrinsic eye
muscles, all of which are protective for the eye.
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35-55
In Summary (cont.)
35.4 The cornea, lens, and fluids focus light on the
retina. The retina converts the image into
nerve impulses that the optic nerve transmits
to the brain for interpretation.
35.5 There are many common diseases and
disorders of the eyes with varied signs,
symptoms, and treatments. Some of these
include astigmatism, dry eye syndrome,
ectropion, entropion, nystagmus, and retinal
detachment.
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in any manner. This document may not be copied, scanned, duplicated, forwarded, distributed, or posted on a website, in whole or part.
35-56
In Summary (cont.)
35.6 There are three parts to the ear. The external ear
includes the auricle or pinna and the external auditory
canal to the tympanic membrane.
The middle ear begins at the tympanic membrane
and ends at the oval window and includes the ear
ossicles.
The inner ear is composed of the labyrinth and
contains the organ of Corti as well as perilymph and
endolymph – the fluids of hearing.
The semicircular canals and vestibule in the inner ear
function in the body’s equilibrium and balance,
sending impulses to the vestibular nerves, which
bring information to the cerebrum for interpretation.
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35-57
In Summary (cont.)
35.7 The outer ear collects sound waves and channels
them to the tympanic membrane, which vibrates. The
vibrations are amplified by the ear ossicles and enter
the inner ear and cochlea. The movements of the
hairs in the cochlea trigger nerve impulses that the
auditory nerve transmits to the brain.
35.8 There are many common diseases and disorders of
the ears with varied signs, symptoms, and treatments.
Some of these include acoustic neuroma, cerumen
impaction, hearing loss, otitis, otitis externa, otitis
media, otitis interna, otosclerosis, and presbycusis.
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35-58
End of Chapter 35
Every closed eye is
not sleeping, and
every open eye is
not seeing.
~ Bill Cosby
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in any manner. This document may not be copied, scanned, duplicated, forwarded, distributed, or posted on a website, in whole or part.